Process of refining chemical pulp



Patented Apr. 15, 1952 PROCESS OF REFINING CHEMICAL PULP Turma Norta and Yrjii Sivola, Imatra, Finland, assignors to Enso-Gutzeit Osakeyhtiii, Helsinki, Finland, a corporation of the Community of Jaaski in the Republic of Finland No Drawing. Application July 31, 1947, Serial No. 765,248. In Sweden October so, 1943 Section 1, Public Law 690, August 8, 1946 Patent expires October 30, 1963 Claims.

When refining chemical pulp according to chemical methods variations in lignin content and viscosity often cause great difficulties in normal refining processes wherefore, generally, very even quality is demanded of chemical pulp intended for some special purpose. One of the properties required of e. g. viscose pulp is that it has a specified viscosity and here no greater variations than 1 cp. are as a rule permissible. In order to reduce and smooth out viscosity the preparation of such viscose pulp has resorted to rigorous hypochlorite treatment. The violence of this treatment is evidenced inter alia by a drop in the percentage amount of the most valuable ingredient'of chemical pulp, i. e. alpha cellulose, and by the rise of the copper number, which designates the amount oxycelluse.

On investigating methods for obviation of the above mentioned defects it was found that if washed, defibered and strained chemical pulp was chlorinated and subsequently heated as a 1-15 per cent aqueous suspension to a temperature somewhat exceeding that of a room and kept at this temperature a specified Period of time dependent on the qaulity of chemical pulp under treatment, ranging in practise from 10- 200 min., the cellulose molecules break up, partly through the agency of acid substances created during chlorination, thus causing a drop in viscosity. As already mentioned, heating must be carried out at a temperature exceeding that of a room, preferably at 40 0.; however it is not advisable to exceed 100 C. because of practical and economical reasons. The heating of chem- .ical pulp can also be applied subsequently to vantages, achieved by the process hereinabove described as compared with the hypochlorite treatment generally used at the moment, are

that inter alia the alpha content of the chemical pulp increases, the pentosan content decreases and the copper number drops.

What we claim is:

1, A process of making refined chemical pulp comprising, selecting washed, defiberecl and strained chemical pulp, chlorinating such pulp at room temperature, forming such pulp into a 1l5% aqueous suspension partially washed with water, and heating such pulp at a temperature above room temperature but not over C. for a period of time of about 10 to 200 minutes at a pH value lower than 5.

2. A process as defined in claim 1 and including adding acid to the partially washed chemical pulp after chlorination in sufiicient amount to lower the pH value under 5.

3. A process as defined in claim 1 and including introducing chlorine into the pulp while the heating is taking place to lower the pH value under 5. l

4. A process of making refined chemical pulp comprising, selecting washed, defibered and strained chemical pulp, chlorinating such pulp at room temperature, then heating such pulp at a temperature above that of room temperature but below 100 C., and continuing that heating for a period of time at about 10 to 200 minutes at a pH value lower than 5.

5. A process of making refined chemical pulp comprising, selecting washed, defibred and strained chemical pulp, chlorinating such pulp at room temperature, subsequently heating such pulp as a 1-15% aqueous suspension at a temperature of approximately 40 C. and continuing such heating for a period of time of from 10 to 200 minutes at a pH value lower than 5.

TURll/IA NORTA. YRJO SIVOLA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,705,897 Bradley Mar. 19, 1929 1,941,154 Richter Dec. 26, 1933 1,967,347 Bayerl July 24, 1934 2,065,395 Richter Dec. 22, 1936 2,070,893 Glass Feb. 16, 1937 2,159,376 Freeman May 23, 1939 2,198,706 Sheldon Apr. 30, 1940 OTHER REFERENCES Cellulose and its Derivatives, by Ott, published by Interscience Publishers, Inc., N. Y., N. Y., 1943, pp. 588-589, 598, 599, and 603. 

1. A PROCESS OF MAKING REFINED CHEMICAL PULP COMPRISING, SELECTING WASHED, DEFIBERED AND STRAINED CHEMICAL PULP, CHLORINATING SUCH PULP AT ROOM TEMPERATURE, FORMING SUCH PULP INTO A 1-15% AQEUOUS SUSPENSION PARTIALLY WASHED WITH WATER, AND HEATING SUCH PULP AT A TEMPERATURE ABOVE ROOM TEMPERATURE BUT NOT OVER 100* C. FOR A PERIOD OF TIME OF ABOUT 10 TO 200 MINUTES AT A PH VALUE LOWER THAN
 5. 